The invention relates to chemical mechanical polishing of substrates, and more particularly to an apparatus for optimizing a polishing pad conditioning process.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes successively more non-planar. This occurs because the distance between the outer surface and the underlying substrate is greatest in regions of the substrate where the least etching has occurred, and least in regions where the greatest etching has occurred. Within a single patterned underlying layer, this non-planar surface comprises a series of peaks and valleys wherein the distance between the highest peak and the lowest valley may be on the order of 7000 to 10,000 Angstroms. With multiple patterned underlying layers, the height difference between the peaks and valleys becomes even more severe, and can reach several microns.
This non-planar outer surface presents a problem for the integrated circuit manufacturer. If the outer surface is non-planar, then photolithographic techniques to pattern photoresist layers might not be suitable, as a non-planar surface can prevent proper focusing of the photolithography apparatus. Therefore, there is a need to periodically planarize this substrate surface to provide a planar layer surface. Planarization, in effect, polishes away a non-planar, outer surface, whether a conductive, semiconductive, or insulative layer, to form a relatively flat, smooth surface. Following planarization, additional layers may be deposited on the outer layer to form interconnect lines between features, or the outer layer may be etched to form vias to lower features.
Chemical mechanical polishing is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head, with the surface of the substrate to be polished exposed. The substrate is then placed against a rotating polishing pad. In addition, the carrier head may rotate to provide additional motion between the substrate and polishing surface. Further, a polishing slurry, including an abrasive and at least one chemically-reactive agent, may be spread on the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate.
Important factors in the chemical mechanical polishing process are: the finish (roughness) and flatness (lack of large scale topography) of the substrate surface, and the polishing rate. Inadequate flatness and finish can produce substrate defects. The polishing rate sets the time needed to polish a layer. Thus, it sets the maximum throughput of the polishing apparatus.
Each polishing pad provides a surface which, in combination with the specific slurry mixture, can provide specific polishing characteristics. Thus, for any material being polished, the pad and slurry combination is theoretically capable of providing a specified finish and flatness on the polished surface. The pad and slurry combination can provide this finish and flatness in a specified polishing time. Additional factors, such as the relative speed between the substrate and pad, and the force pressing the substrate against the pad, affect the polishing rate, finish and flatness.
Because inadequate flatness and finish can create defective substrates, the selection of a polishing pad and slurry combination is usually dictated by the required finish and flatness. Given these constraints, the polishing time needed to achieve the required finish and flatness sets the maximum throughput of the polishing apparatus.
An additional limitation on polishing throughput is xe2x80x9cglazingxe2x80x9d of the polishing pad. Glazing occurs when the polishing pad is heated and compressed in regions where the substrate is pressed against it. The peaks of the polishing pad are pressed down and the pits of the polishing pad are filled up, so the surface of the polishing pad becomes smoother and less abrasive. As a result, the polishing time required to polish a substrate increases. Therefore, the polishing pad surface must be periodically returned to an abrasive condition, or xe2x80x9cconditionedxe2x80x9d, to maintain a high throughput.
Another consideration in the production of integrated circuits is process and product stability. To achieve a low defect rate, each successive substrate should be polished under similar conditions. Each substrate should be polished by approximately the same amount so that each integrated circuit is substantially identical.
An apparatus for measuring the profile of a polishing pad in a chemical-mechanical polishing system has been described in U.S. Pat. No. 5,875,559. The apparatus generates pad profiles that include the measurement of the thickness of the polishing pad which may be used to optimize the polishing process parameters or to select a conditioning process. The pad profiler generates plots of the surface profile of the polishing pad. These plots may be used by machine operators to select a conditioning process. There is no automatic control or closed loop control of the conditioning process. Hence, if any changes need to be made to the conditioning process based on the surface profiles generated by the pad profiler, these changes would be made in a separate operation by the machine operator.
Another apparatus for measuring the profile of a pad has been discussed in U.S. Pat. No. 5,618,447. In an unshown embodiment, a processor is described as being operatively coupled to a pad conditioning device. The processor selectively controls the pad conditioning device according to the contour measurements from the sensor to change the contour of the polishing surface of the pad. After the pad has been selectively conditioned, the contour of the new polishing surface is preferably re-measured to determine whether the new polishing surface has the desired post-conditioning contour.
One of the drawbacks to the process discussed in U.S. Pat. No. 5,618,447 is that the measurement of the pad profile is not preformed in-situ such that the pad conditioning process can be changed during the conditioning process. It is only after the conditioning process is complete that a remeasurement of the pad profile is performed. Hence, since there is no immediate feedback and closed loop control of the conditioning process, it is possible for the pad to be improperly conditioned at any given time.
In view of the foregoing, there is a need for a chemical-mechanical polishing apparatus that provides precise and immediate control of the pad conditioning process.
There is a need for a method and apparatus to control a pad conditioning process automatically in a manner that provides precise and immediate control of the pad conditioning process.
These and other needs are met by embodiments of the present invention which provide an arrangement for conditioning a polishing pad of a chemical-mechanical polishing apparatus. The arrangement includes a pad conditioning head and a disk carrier on the pad conditioning head. The disk carrier is configured to receive and carry a polishing pad conditioning disk. The arrangement includes an arm having first and second distal ends, the pad conditioning head being coupled to the first distal end. An arm support is coupled to the second distal end of the arm. The arm support is configured to move the arm to position a conditioning disk carried by the disk carrier against a polishing pad with a controlled amount of down force against the polishing pad. A down force sensor measures the down force exerted by the pad conditioning head through a conditioning disk against a polishing pad. A controller receives the down force measurements from the down force sensor and controls the arm support to controllably vary the down force exerted by the pad conditioning head.
By providing an arm support that is configured to move an arm to position a conditioning disk against a polishing pad with a controlled amount of down force, the present invention provides a precise and in situ arrangement for controlling the conditioning of the polishing pad. The use of the arm support to position the conditioning disk against the polishing pad and control the amount of down force through the arm support, allows the conditioning head to be simplified in construction as it does not require a disk carrier that moves vertically away from the arm support towards the polishing pad. Instead, the control of the down force is provided at the arm support. The disk carrier therefore only needs to make a rotary motion.
The earlier stated needs are also met by other embodiments of the present invention which provide a chemical-mechanical polishing apparatus comprising a platen for supporting a polishing pad, a wafer carrier for carrying a wafer and positioning the wafer against the polishing pad to polish the wafer, and a conditioning arrangement for conditioning a polishing pad. This conditioning arrangement includes a pad conditioning head, with a disk carrier on the pad conditioning head. The disk carrier is configured to receive and carry a polishing pad conditioning disk. The polishing pad conditioning arrangement also includes an arm having first and second distal ends, with the pad conditioning head being coupled to the first distal end. An arm support is coupled to the second distal end of the arm. The arm support is configured to move the arm to position a conditioning disk carried by the disk carrier against a polishing pad with a controlled amount of down force against the polishing pad. A down force sensor measures the down force exerted by the pad conditioning head through a conditioning disk against a polishing pad. A controller receives the down force measurements from the down force sensor and controls the arm support to controllably vary the down force exerted by the pad conditioning head.
The earlier stated needs are also met by another embodiment of the present invention which provides a method of conditioning a polishing pad of a chemical-mechanical polishing apparatus comprising the steps of determining a wear condition of a polishing pad and positioning a conditioning head over a polishing surface of the polishing pad through an arm arrangement that is connected to the apparatus and to the conditioning head. A conditioning disk carried by the conditioning head is positioned onto the polishing pad with a controlled down force of the conditioning disk against the polishing surface. The down force is measured with a sensor located in the arm arrangement and the polishing pad is conditioned. The down force of the conditioning disk is controlled during the conditioning of the polishing pad as a function of the determined wear condition of the polishing pad and the measured down force of the conditioning disk on the polishing pad.
The earlier stated needs and others are met by another embodiment of the present invention which provides an arrangement for conditioning a polishing pad of a chemical-mechanical polishing apparatus. This arrangement includes a pad conditioning head, a disk carrier on the pad conditioning head, the disk carrier being configured to receive and carry a polishing pad conditioning disk. An arm is provided having first and second distal ends, the pad conditioning head being coupled to the first distal end. An arm support is coupled to the second distal end of the arm. The arm support has a rotary actuator to rotate the arm to position a conditioning disk carried by the disk carrier over a polishing pad. The arm support also has a vertical actuator to move the arm in a direction normal to a polishing pad to position a polishing pad conditioning disk carried by the disk carrier against a polishing pad.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein embodiments of the present invention are described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.